1. FIELD OF THE INVENTION
The present invention relates to an ignition system for internal combustion engines in which the energization time of an ignition coil is controlled.
2. DESCRIPTION OF THE RELATED ART
As examples of a conventional ignition system for internal combustion engines of the type described above, there are a system in which a storage quantity of storing means is gradually increased through a predetermined angle from the reception of an ignition signal to an ignition timing, and then the thus increased storage quantity is decreased, and the decrease rate of the storage quantity is changed after the lapse of a predetermined time so that the energization of an ignition coil is initiated at a time point when the storage quantity has been decreased to its initial value (for example, as disclosed in Japanese Patent Unexamined Publication No. 55-23394 (1980)); a system in which a storage quantity of storing means is gradually increased through a predetermined angle from an ignition timing, and then, after a lapse of a predetermined time, the thus increased storage quantity is gradually decreased without changing the storage quantity decrease rate so that the energization of an ignition coil is initiated at a time point when the storage quantity has been decreased to a set value which is larger than its initial value (for example, as disclosed in U.S. Pat. No. 3,937,193), etc.
In the former one of the foregoing conventional ignition systems, however, the decrease rate of the storage quantity is changed after a predetermined time has elapsed from the ignition timing, so that it is necessary to use a monostable circuit or a counter for detecting a time point when the predetermined time has elapsed from the ignition timing. Accordingly, this system has a disadvantage that the circuit of this system becomes extremely large in scale.
In the latter one of the foregoing conventional ignition systems, on the other hand, the storage quantity is gradually decreased from a predetermined angular position immediately before a succeeding ignition timing so that the energization of an ignition coil is initiated at a time point when the storage quantity has reached a predetermined value. Accordingly, when the ignition timing is advanced upon quick acceleration of an internal combustion engine, etc., an ignition signal for turning off a power transistor may be applied before a sufficient primary current flow is established in an ignition coil, so that this system has a disadvantage that a high voltage for ignition cannot be generated in the ignition coil.